1. Field of the Invention
The invention relates to an apparatus for fluid distribution in a substrate processing system, and more particularly, to a gas distribution plate in a semiconductor wafer processing system.
2. Background of the Invention
Gas distribution plates (GDP""s) are used for delivering gases from a source to a process chamber. The gases are used for various phases of semiconductor device manufacturing including etching and chemical vapor deposition (CVD). The gases are heated, especially in metal etching process, to temperatures in the range of 600-2000xc2x0 C. Typically, a GDP is fabricated from quartz and U.S. Pat. No. 5,614,026 discloses such a device for uniformly distributing process gas over a semiconductor surface in a plasma-based stripping process. Quartz exhibits good mechanical strength when exposed to thermal gradients. More specifically, the hot gases are usually delivered from the source to the GDP via a 1 in. diameter pipe. These gases then flow across the GDP (typically a single plate 8 in. diameter) and pass through openings in the GDP. The center of the GDP, receiving the greatest concentration of hot gases, is heated more than points radially outward therefrom. The change in temperature across the GDP causes a stress in the atomic bonds of quartz. This stress however does not exceed the mechanical strength of the quartz; therefore, it does not break. However, in certain circumstances, a fluorine-based gas is introduced to the process chamber for etching portions of a substrate during semiconductor device formation. Unfortunately, quartz is etched by fluorine. As such, two undesirable conditions occur. First, quartz is released into the chamber environment, which causes contamination in the substrate. Second, the quality and integrity of the GDP is compromised as a result of the etching.
Alternately, the GDP is fabricated from a ceramic material such as oxides including alumina (Al2O3), magnesium oxide (MgO2) and the like. Ceramic materials have an advantage over quartz when it is necessary to use a fluorine-based active species (gas) for substrate processing. Unfortunately, the mechanical strength of such ceramic material GDP is exceeded by the thermal stresses imposed by heating and/or power application when creating or sustaining a plasma. Breakage or fracturing of the ceramic material undesirably introduces contaminants into the chamber during processing. The mechanical strength of a ceramic GDP can be increased by increasing the thickness of the plate; however, a xe2x80x9cfirst wafer effectxe2x80x9d undesirably results. The xe2x80x9cfirst water effectxe2x80x9d is a condition whereby a first number of wafers at the beginning of a process cycle are not properly processed due to a variety of conditions such as insufficient preheating of the GDP or poor active species concentration at the substrate surface. In other words, as plate thickness increases, the path to the substrate surface and recombination rate of the active species increases thereby reducing active species concentration. Moreover, in each of the types of GDPs discussed, there are no provisions in the construction or design to alleviate the thermal stress or etching problems.
Therefore, there is a need in the art for a GDP that exhibits high mechanical strength under thermal gradients, and is unaffected by the atmosphere that it services.